(a) Field
The subject matter disclosed generally relates to an electric wheel.
(b) Related Prior Art
Internal combustion engines, particularly those of the reciprocating piston type, currently propel most vehicles. Such engines are relatively efficient, compact, lightweight, and inexpensive mechanisms by which to convert highly concentrated energy in the form of fuel into useful mechanical power. The primary problem with conventional gasoline or diesel combustion engines is that they require fossil fuels that are not renewable and contribute to pollution. Consequently, a fuel that is renewable and does not contribute to pollution is desirable.
One alternative to combustion vehicles is hybrid vehicles. Hybrid vehicles include an electrical power source in addition to the internal combustion engine. In particular, the hybrid vehicle may include a gasoline engine, fuel tank, electric motor, batteries, transmission, and electric generator. Various approaches to combining the electrical power source and the internal combustion engine are known, such as a parallel hybrid in which the engine and electric motor can both simultaneously drive the transmission and the series hybrid in which the engine drives the electric generator which charges the batteries or powers the electric motor to drive the transmission.
Some hybrid vehicles are configured to allow connecting the vehicle to an external electric power supply, that is, the hybrid vehicle may be plugged in for charging. There are also battery electric vehicles that are fully powered by the electrical power source. The battery electric vehicle is configured to allow connecting the vehicle to an external power supply, that is, the battery electric vehicle may be plugged in for charging.
Each of the above vehicles use a central engine/motor and requires a transmission in order to transmit the rotation power from the engine/motor to the wheels.
A typical mechanical transmission for fuel powered vehicles allows some freedom in engine operation, usually through alternate selection of five or six different drive ratios, a neutral selection that allows the engine to operate accessories with the vehicle stationary, and clutches or a torque converter for smooth transitions between driving ratios and to start the vehicle from rest with the engine turning. Transmission gear selection typically allows power from the engine to be delivered to the rest of the drive system with a ratio of torque multiplication and speed reduction.
No transmission system is ever completely efficient and there is always a percentage of energy lost in friction in the axle, gearing, clutch and the like, especially when the vehicle is equipped with an all wheel traction mechanism (AWD).
Another problem associated with conventional vehicles is that substantial amount of the car's weight and storage space is taken for the engine/motor and the transmission system, not to mention the maintenance and replacement parts which are provided in large numbers in each vehicle.
Attempts have been made to overcome these problems by providing in-wheel motors whereby one or more wheels in the vehicle would comprise their own motor, thereby alleviating the need for a central motor and a transmission system. An example for such attempts is provided in co-owned and co-invented International Application No. PCT/CA2012/000673. PCT/CA2012/000673 (which is incorporated herein by reference in its entirety) describes a wheel assembly comprising a plurality of stator units coaxially provided within a rotor. The stator units comprise a plurality of spokes co-centrically provided around a hub/shaft and a coil provided around at least a portion of the spokes for generating an electrical field. The rotor comprises a plurality of magnets provided on an inner periphery of the rotor facing the spokes. The rotor is rotatably attached to the hub/shaft of the stator for rotating around the stator units when the coils are activated. The coils and/or the stator units may be selectively activated and deactivated to avoid overheating.
This type of motors reduces the friction losses experienced in a conventional transmission but they still experience magnetic losses. Additionally, while the overheating in these motors is reduced, it is not completely eliminated and still imposes limitations especially if the type of driving involves extended acceleration and deceleration e.g. if the vehicle is driven in a sport mode or used in racing etc.
Therefore there is a need for an improved wheel motor which is at the same efficient and also allows for extended use without overheating.